A contemporary wireless communication system, such as distributed antenna system, includes a plurality of remote units distributed throughout a service area (e.g., a building) to provide coverage within the service area of the system. In particular, each remote antenna unit is typically coupled to a master unit, which, in turn, is coupled to at least one single-input- and single-output (“SISO”) base transceiver station (“BTS,” or more simply, “base station”).
Each remote unit generally transceives wireless signals with a number of wireless devices, such as a telephone devices or computing devices in the proximity of the remote unit. In particular, the wireless signals from each remote unit are associated with one or more BTSs. Thus, the wireless devices may communicate with the system BTS's through any of the wireless signals from the remote units.
To improve such wireless communications, Multiple-Input/Multiple-Output (“MIMO”) technology might be utilized to provide advanced solutions for performance enhancement and capacity in broadband wireless communication systems. It has been shown that substantial improvements may be realized utilizing a MIMO technique with respect to the traditional SISO systems. MIMO systems have capabilities that allow them to fully exploit the multi-path richness of a wireless channel. This is in contrast with traditional techniques that try to counteract multi-path effects rather than embrace them. MIMO systems generally rely upon multi-element antennas at both of the ends of the communication links, such as at the base station and also in the mobile device. In addition to desirable beam-forming and diversity characteristics, MIMO systems also may provide multiplexing gain, which allows multi data streams to be transmitted over spatially-independent parallel sub-channels. This may lead to a significant increase either in the system capacity or in the data throughput to each wireless device. Generally, distributed antenna systems cannot take advantage of MIMO technology because they are just designed to provide SISO wireless coverage.
For example, in traditional distributed systems, a wireless device communicates with only one of the remote units, the signals of which are typically isolated from signals of other remote units using base station sectorization techniques. In this manner, the signals from different remote units avoid interference due to overlap of coverage areas. The wireless signals from each remote unit are typically at the same frequency and carry the same data.
Additional problems occur with a distributed antenna system disposed within an indoor environment. For example, indoor environments are often associated with increased amounts of multipath richness. Generally, internal building components (e.g., columns, pipes, walls, doors) as well as objects inside that building (e.g., computers, desks, fixtures) cause an increasing of the scattering phenomena. Also for example, SISO distributed antenna systems are typically designed to provide wireless coverage within a particular indoor environment. However, because of the multipath richness, antenna shadowing can occur depending upon the particular layout, user position, and obstacles within that indoor environment.
Accordingly, it is desirable to improve upon existing distributed antenna systems taking advantage of MIMO technology in distributed wireless environments which may benefit such propagation conditions.